


Unspoken Words

by Complete_Otakuness



Series: Dr. STONE Mermaid AU [2]
Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: Alternate Universe - Merpeople, Alternate Universe - Sirens, But also, Canonical Character Death, I'll add more tags as the story progresses, M/M, Mermaid!Senku, Minor Character Death, because she is a little girl, he still doesn't like physical contact, i almost forgot those tags, i was inspired after reading Senku's bizarre adventures by Cherin, like...how would that work?, mirai goes to school, senku sings when he's sad, siren hair is weird, this is what happens when you have a goddamn plot bunny, tsukasa works very hard for his sister, was lowkey interested in the idea of a siren wanting to go to space, whoops
Language: English
Status: In-Progress
Published: 2020-04-27
Updated: 2020-07-04
Packaged: 2021-03-01 20:13:46
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 3,443
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23882824
Author URL: https://archiveofourown.org/users/Complete_Otakuness/pseuds/Complete_Otakuness
Summary: Senku, loving science, wants to go to space but unfortunately is a siren. Tsukasa, being a good big brother, wants Mirai to have a good life but unfortunately balances school and three jobs. Will these two ever catch a break?In other words, the Tsukasen Mermaid AU that I wanted to write. And sorry about the bad summary, I wasn't sure how to put it together.
Relationships: Asagiri Gen & Ishigami Senkuu, Ishigami Senkuu & Ogawa Yuzuriha & Ooki Taiju, Ishigami Senkuu & Shishiou Tsukasa, Ishigami Senkuu/Shishiou Tsukasa, Ogawa Yuzuriha/Ooki Taiju, Shishiou Mirai & Ishigami Senkuu, Shishiou Tsukasa & Shishiou Mirai
Series: Dr. STONE Mermaid AU [2]
Series URL: https://archiveofourown.org/series/1975693
Comments: 6
Kudos: 74





	1. Prologue

Senku watched as a teenage boy and a little girl played together on a precipice that leaned, not far, over the calm blue of the ocean. It seemed they were collecting shells for a necklace. The little girl looked like she was over the moon and the teen, while happy that she was having fun, was also anxious and kept telling her to be careful and stop running everywhere.

The merman smiled to himself and continued trying to chip away at the rocks that poked out of the water just underneath the overhang. They were rich in minerals that he needed for an experiment and he didn’t care if he almost got spotted to get them. He didn’t bring his tools for nothing, afterall.

A short moment later, however, a short gasp and a scream sounded above. Senku, startled, looked up to see the shells previously in the girl’s arms flying everywhere. She had slipped on the rocks and off the crag. The teenager was reaching for her but Senku could already tell he wouldn’t catch her in time.

Both boys could only stare in shock (and maybe a little horror) as the girl fell into the water. Senku was relieved that she hadn’t fallen on any of the rocks, if by a margin of about a meter. Instead she had hit the water. It wasn’t a far drop and the water was fairly calm so it probably only stung a bit. His relief quickly turned to panic as the little girl began splashing around and sinking helplessly. She didn’t know how to swim? Why didn’t she know how to swim?

Abandoning his tools, Senku dove toward the sinking girl. He grabbed her and pulled her up. When their heads broke the surface the little girl gasped for air, before finding the face of her savior. When she saw him, a bright smile wrestled its way onto her terrified face.

Senku had begun swimming his way to a small pocket beach in the midst of some tall rocks when the girl spoke, “You’re a mermaid! I love mermaids!”

He stared at her a moment before smirking, “Is that so?”

The little girl nodded vigorously, “Uh-huh! I was even collecting shells to make a mermaid necklace like yours right before I fell!”

“Like mine?” Senku made it to the beach and set her down on the sand before taking off his necklace. The girl stared at it in awe, her eyes wide.

He placed it around her neck, only causing her eyes to grow wider, and said, “Well, I hope this will compensate for your lost progress. And try not to make a habit of falling off big rocks, got it?”

The little girl looked like she was about to implode, “Thank you! I’ll cherish this forever!" Senku chuckled and faintly hoped his warning didn’t go in one ear and out the other. 

Then a boy's voice was carried over the rocks, “Mirai? Mirai hold on I’m coming!” Senku rolled his eyes. Mirai’s older brother had decided not to jump off the precipice after her and had taken a safer route down to the water level. Lucky for Senku (he wanted as little people to see him as possible), but unlucky for Mirai’s brother. 

Mirai only giggled and shouted back, “Big brother, I’m alright! I’m over here!”

“Wh- Mirai! Stay there, I’ll be right over!”

“Okay!”

Senku smiled and patted her on the head as he slid back into the water, “That sounds like my que to leave, take care.” He waved and then turned to swim into deeper water.

********************************************************************************************************

Tsukasa had no idea how his sister had made it to land by herself. She couldn’t swim, afterall. He sighed in exasperation, this is what he gets for saving money on swimming lessons.

When he made it over yet another rock, he decided to try and look for Mirai. Tsukasa heard a splash and turned his head in the direction of the ocean just in time to see a huge green tail disappear under the water. He froze. That… that couldn’t be right, could it? A giant sea creature didn’t just swim away from the place Mirai probably was. Did it? Tsukasa looked down to see his sister not far off, waving in the direction he saw the creature. Did it?!


	2. A few years later

Tsukasa couldn’t sleep. He didn’t know why, though. He just felt restless. He had done the groceries, ironed Mirai’s freshly washed uniform for school, and had taken some sleeping pills. There really should be nothing keeping him up.

But that didn’t change the simple fact that Tsukasa couldn’t sleep. So here he was, sitting on the same crag that he and Mirai had been on when they tried to collect seashells for her mermaid princess necklace (she never did tell him how she had gotten the one she wore now). 

It really was a nice spot if you didn’t go too near the edge. There was a slight breeze that ruffled Tsukasa’s long hair as he looked out over the spot where the sky met the sea. The half moon reflected in the water and it’s light bounced off the rock and boulders, both on land and sticking out of the sea. Everything he could see was illuminated in a very soft glow. Tsukasa wrapped his arms around his knees and sucked in a breath of salty ocean air.

When he heard a splash and a slap noise, he didn’t think much of it. He just assumed it was water splashing up and hitting the rocks, causing a disturbance. But when he heard a loud sigh and the thump of a weighted object being put down, that’s when he got curious. Who, besides him, was here this late at night?

As Tsukasa scooted a little closer to the edge, a sharp clanging and the gentle noise of someone singing filled the air. The song didn’t have any lyrics (or at the very least, in any language Tsukasa knew of) but it was full of emotions. Emotions that Tsukasa realised probably didn’t even need words.

When he got to the ledge, Tsukasa risked a peek down, towards the rocks that lay just underneath the precipice. The ‘creature’ looked almost unreal. Water dripped down from his shoulder-length hair which was, oddly enough, a gradient of white to green at the tips. His skin was pale and gradually faded at the waist into the emerald green scales of a tail. There were two thin fins that began at his hips and ended just before the huge pale fin at the end of his tail.

Tsukasa couldn’t believe what he was seeing, but the siren was there. He was there, sitting on a rock and singing while he broke off chunks of another boulder close by. His bag, full of miscellaneous stuff, was leaning against him.

The merman looked hard at work, gathering stone fragments, but his mind seemed to be elsewhere. If his song was anything to go by. It sounded sad, lost, as if he didn’t know how to go on. But he would anyway, he had to. He wouldn’t lose motivation.

Tsukasa felt himself almost being moved to tears and then shook himself. Living so near to the ocean and working a part time job near there, he had heard a few of the sailors tell stories to one another. Stories of hungry sirens singing songs of despair to lure sympathetic fishermen into the water and to their deaths. Naturally, Tsukasa had thought the tales were ridiculous and even the boatmen had laughed it off. But what if those stories were true? The evidence was right in front of him.

When the siren began to pack up, Tsukasa thought it was time for him to leave as well. He did have a wrestling match the next day after all. He had nearly forgotten about it though. 

He watched as the merman slowly sank down into the water, his satchel hanging off his shoulder. The siren sang a final ‘verse’ and turned around to face the moon hanging in the midnight sky. It made his scarlet eyes glow and danced along the outline of his body, which was now half-way submerged in water. His hair had dried in an almost comical way, with it standing straight up like the quills of a porcupine.

Tsukasa quickly backed away from the ledge -he couldn’t be sure if the mer had seen him- and heard a content sigh. The kind of sigh that came from finishing a job and having a weight off your shoulders. Then splashing and soon Tsukasa could see the siren swimming away and diving into deep water. The last thing he saw was his tail, every scale a diamond that could’ve been plucked from the stars.

It truly was a beautiful sight, if not also vaguely familiar. Tsukasa got up from his spot and began to slowly trudge the two blocks to his home where Mirai was -hopefully- sleeping peacefully. Nostalgia bogged him down, and he didn’t want to go back to everyday life after what he saw. But the fantastical moment was over.

‘Over sure,’ Tsukasa mused, ‘But never forgotten. I just wish I knew why it felt so familiar.’


	3. The Next Day

“Senku!” Taiju yelled excitedly. The mer looked up over the rock he was leaning against to see his meat-headed friend being hastily quieted by said friend’s girlfriend.

“Taiju shush, we don’t know if anyone can hear us or not,” Yuzuriha looked anxiously over her shoulder.

Senku chuckled. “I’m pretty sure everyone can hear him Yuzuriha. If their hearing hasn’t been damaged beyond repair beforehand.”

She sighed in exasperation. “Good point.” The two humans climbed over the rocks in their way to sit in front of the water. There was a small stretch of sand that lines the coast -it was mostly covered in boulders- and this was where the three usually met in the morning before school. Taiju and Yuzuriha positioned themselves in a way that would shield Senku from the view of any passersby. It looked like they were on a secret date which -Senku supposed- had been true the first time they met Senku.

“Oh Senku! I got that book you asked for!” Senku turned to look at Taiju and watched as he opened his school bag to pull out said book.

A smirk found its way to Senku’s face, “Thanks, I’ve been waiting a whole week for that one.” He eagerly grabbed it and flipped to the first page. The book was titled Fourteen Billion Years of Cosmic Evolution by two authors named Neil deGrasse Tyson and Donald Goldsmith. Senku -being a siren- had no idea who either of these people were. He didn’t care if they were a big deal, all he cared about was whether they knew their stuff or not. 

“Alright Senku, class starts soon so we have to get going. Hope you enjoy your book and we’ll see you after school, alright?” Yuzuriha might as well have been talking to a brick wall with the way Senku just waved her off and grunted. Nonetheless, she and Taiju knew how Senku was when he got his hands on new reading material and decided they needed to head to school before they were late. The two smiled at each other and linked hands as they walked away.

********************************************************************************************************

“Senku-chaaaannn come ooonnn!” Gen tugged at his friend’s arm lightly, trying to lead him back to deeper water. His purpureus tail swished in the water, making small splashes. 

“Wha- Stop you’ll get the pages wet! Books aren’t like the scrolls or tablets we use at the village!” Senku pulled his arm out of Gen’s grip and smiled, his eyes sparkling with excitement, “You want to know what book I have this time?”

Gen sighed, “I probably won’t get it, Senku-chan. The stuff you read is on a higher level than any of the science I learned when I still went to highschool. But, if you’re going to explain it, could we at least go farther out? I’m still nervous about being so close to the shore.”

Senku rolled his eyes, “Fine, if you’re so worried about it, let’s go. Just let me hide my book first.” He understood why Gen was so cautious but easily could’ve sat for hours to read in the sun. There weren’t that many people who frequented the shore and most who did already knew that Senku and Gen were there. ‘Most’ being Taiju and Yuzuriha.

The only other person was a vaguely familiar man with long brown hair and large stature.   
He jogged along the coast regularly, once when the sun rose and again when it set. Senku saw him a few times when he swam to the beach before night fell to watch a meteor shower and the morning after when he had begun packing up his equipment.

“How’re Taiju-chan and Yuzuriha-chan? I’m assuming you got the book from them?” Gen asked as they swam out further. 

“Well, their relationship seems well enough but Taiju asked me -of all people- to help him study with a math test a few days ago. Like I would know what the test is on, I’m not a highschool student!”

“So? Did you help him study?”

“Of course I did. And, surprisingly, I actually knew some of the stuff on his study guide. I guess all of my reading paid off.” Senku grinned proudly as his head became submerged and the pair descended.

“Well, your intellect is hard to beat. I’d be willing to bet you’d be at the top of your class if you actually went to highschool,” Gen mused with a thoughtful expression on his face. “Come to think of it, Senku-chan, why are you and Chrome-chan so interested in science anyway?”

A smirk showed itself on Senku’s face, “Chrome has an unquenchable thirst for knowledge, I supposed the same could be said for me.”

“Yeah, but why do you want to go to space? What about space specifically is so amazing?”  
Gen pressed, his eyebrows slightly furrowed.

“Humans don’t actually know much about space or the ocean, correct? Or, at least, not as much as they do about land. We,” Senku gestured to both himself and Gen, “live in the ocean, we know what creatures lurk in the darkness of the depths. So what else is there to explore but space?”

Gen let out a sigh, “I supposed I’m not going to get the entire truth out of you?”

“What are you talking about? I really do want to go to space you know.” Senku put on an innocent smile, “How’ve you been adjusting here? Has Kohaku stopped giving you ‘the look’ yet?”

Gen chuckled. Ever since he had joined Ishigami Village, Kohaku, along with some others, had all looked at him with the same expression. A look of plain distrust. As a result, Gen began by distancing himself quite a bit, though most villagers had warmed up to him. Especially an old mer named Kaseki. It was very apparent that he thought of Gen as the grandson he never had and was the first -besides Senku, or course- to take him under his fin and teach him the basics of mermaid lifestyles. 

“I’ve been doing well, surprisingly. In the beginning, I was overwhelmed but thanks to Old Man Kaseki I’ve gotten the hang of living here. And I think everyone has gotten used to me too.”

“That’s good,” For a second, Gen thought he caught a glimpse of a relieved expression on Senku’s face before it disappeared a millisecond later. What replaced it was a smirk. “Though, you think you could sneak back into your old house and scrounge up anything of use? I wouldn’t have to worry about ruining another library book.”

Gen frowned, “That wouldn’t work, I sold most of my belongings along with my house. Besides, I don’t think it’s a good idea to show up out of the blue after announcing that I was moving to the U.S. to pursue my mentalist career.”

“Yeah, you’re right. It would be nice not to care whether I get water stains on a few pages or not.”

“You keep mentioning that. Did something happen in particular?”

“Not really. Except, the first time Taiju lent me a library book, it was the morning of the day he was supposed to return it. I had an agriculture project to lead that day and couldn’t stay on the beach to read all day like I had previously done. So Taiju suggested I read it in my spare time -particularly the breaks in between farming- and give it back to him after school. We realized our mistake too late when Taiju began walking away and I was halfway submerged in the water. A classic of not-paying-attention-to-what-you’re-doing.”

“Who would’ve thought that the oh-so-wise-and-brilliant leader of the village could make such a mistake.” Gen giggled slightly.

“Yeah, that was back when I was still studying meteorology.”

“The good old days, right?” He joked.

“Yeah… Well, here we are.” Gen glanced in front of him and realized Senku was right. The pair had arrived at the siren settlement, Ishigami Village.


	4. The Same Day

Tsukasa was making breakfast when Mirai woke up. She rose at roughly the same time every morning -6:45 to 7:00- so Tsukasa always tried to have breakfast ready by that time.

‘Yes,’ Tsukasa reminded himself, ‘This is a normal day. You’ll just have to worry about that later.’

Mirai yawned, still in her pajamas. “ ‘Ood morning big brother.” 

“Good morning Mirai.” Tsukasa smiled a soft smile and set her bowl of egg rice on the kitchen table. “Breakfast is ready.”

“Thanks.” Mirai sat down and began to shovel food into her mouth. After a bit, when she got up to wash her bowl in the sink, Tsukasa decided to ask her the question that was on his mind.

“Hey Mirai, you know that necklace you always wear?”

Mirai put her bowl on the drying rack and turned to him with an eyebrow raised, “Yeah, what about it?”

“Where’d you get it again?”

She gave him an ‘are you serious?’ look and fiddled with the shells strung on the necklace before replying with, “A friend gave it to me after I was sad that I couldn’t make one myself. Didn’t I tell you this already?”

“Yes, I just wanted to make sure.”

“Sure of what?” Tsukasa bit his lip. She had already seen him, hadn’t she? But what if the one Tsukasa saw was a different siren than the one Mirai met? That would be dangerous, Tsukasa had already felt the effects of a siren’s song and it hadn’t even been directed at him!

“Nothing, it’s just that you wear it all the time. Do you really like it that much?” Tsukasa just had to lie to her, he didn’t want to risk her getting hurt or, what sirens were most notorious for, drowned.

A wide smile replaced the suspicious look from earlier as Mirai exclaimed, “I love it! I’ll never take it off” This made Tsukasa smile as well and he nodded. “I’m going to go get ready now! Good luck with school and your job, big brother!”

Tsukasa nodded again, “I’ll clean up here and then be on my way. Have a safe walk to school.”

Mirai poked her head out of the doorway to her room and frowned, “Are you sure you don’t need help? You might be late to school. I coud wait before I head out.” She walked out a few seconds later in her school uniform.

“No, don’t worry, I’ve got it. Your friends are waiting for you right?” Tsukasa grabbed her school bag for her and waited for her to make her way over to the front door.

“I guess so. See you later then, big brother!” Slipping on her shoes and taking the bag that Tsukasa handed to her, Mirai hugged him goodbye and walked out the door. Making sure she crossed the street safely, Tsukasa closed the front door and swiped a towel to start wiping down the table.

A few minutes later, he was gathering his shoes and bag at the door too. Waiting outside for him was his bike, locked up and leaning against the fence in front of the house. Tsukasa took a deep breath and mentally prepared himself for another tiring day of classes, exercise, and -today at least- his job at a small but popular ramen shop.

Freeing his bike from its confines and pedaling away after locking the front door, Tsukasa knew it would be a long day. ‘Just like any other,’ he supposed.

**Notes for the Chapter:**

> The 'egg rice' I mentioned that Tsukasa made for Mirai is called Tamago Kake Gohan but I thought the name was a little lengthy so I changed it.


End file.
